The principles of adhesion, wherein the molecules of one substance bind or are attracted to molecules of another substance necessarily play a significant role in dentistry. For example, the adhesion process directly affects the dental restoration of teeth. In brief, adhesion is a surface attachment process wherein the attachment of one substance (e.g., resin or resin composite material) to another (e.g., enamel or dentin on a tooth structure) can be accomplished by mechanical bonding. As applied to dentistry, mechanical bonding involves the penetration of an adhesive or resin into crevices on the surface of the tooth structure.
Current examples of mechanical bonding used in dentistry includes the use of resin restorative materials. Nevertheless, these resins are not capable of truly adhering to a tooth structure. In a method known to those skilled in the art, a fluid or semi-viscous resin is used to create a mechanical bond between the resin and the tooth structure because the flowing resin readily penetrates into the surface defects (i.e., crevices) of the tooth structure. Subsequently, once the fluid resin hardens, the plurality of resin projections embedded in the tooth surface provides a base for mechanical attachment. The procedure for using a fluid or semi-viscous liquid (e.g., resin or adhesive) is referred to as wetting. If the fluid does not wet the entire surface of the affected area of the tooth, adhesion between, for example, resin and the tooth structure will be negligible or non-existent. Poor adhesion or non-adhesion between the tooth structure and a restorative material often results in leakage adjacent to the restored area. This leakage typically leads to staining, secondary tooth decay, and irritation to the pulp of the tooth structure. As discussed below, a number of factors such as the cleanliness of the surface influence the ability of an adhesive or resin to wet the surface of the tooth surface.
A popular technique for applying resin restorative materials includes treating the enamel of the tooth structure with phosphoric acid prior to applying the resin. This technique is commonly referred to as the acid-etching technique. The acid creates microscopic pores in the enamel surface of the tooth structure into which the resin subsequently flows when delivered into the etched area. As referenced above, the resin projections jutting into the pores in the enamel surface of the tooth enhance the mechanical retention of the restoration upon hardening, thereby reducing the possibility of interfacial marginal leakage.
The most significant problem associated with bonding resins to the tooth structure during restorative procedures is contamination by water or a patient's saliva. During routine dental restorative procedures, a dentist must constantly attempt to keep the affected area of a tooth dry. Although tools such as dental dams, air jets, and suction devices are used to prevent saliva from encroaching upon the affected area, some saliva inevitably reaches portions of the affected area during the restorative procedure. This situation is especially true during dental restorations whereby the dentist must restore the tooth in a stepwise fashion involving multiple dental instruments. During a routine repair of a decayed area on the tooth surface, the dentist must first retrieve an acid application tool (e.g., syringe) from a storage rack, etch the decayed area for approximately fifteen seconds, and then replace the acid applicator on the storage rack. Upon etching the tooth, the dentist retrieves an air and water syringe from the storage rack, and rinses the acid etchant off the enamel with a stream of water for approximately ten to twenty seconds. Next, the dentist applies air to the affected area in order to dry the same while attempting to exclude all moisture. Upon returning the air and water syringe to the rack, the dentist must quickly retrieve a resin applicator from the storage rack and apply resins to the prepared area before the patient's saliva reaches the prepared area. The etched surface must be kept clean and dry until the dentist applies the resin in order to form a sufficient bond. Upon returning the resin applicator to the storage rack, the dentist retrieves a light source and exposes the affected area in order to cure the resin. Inevitably, some moisture will reach the affected area during the lengthy process described above as a result of the patient moving his tongue over the affected area, attempting to swallow, or partially closing the mouth.
Adding to the difficulty of keeping the prepared area dry is the fact that the inorganic bonds of the tooth structure have a strong affinity for water. As result, the presence of at least a small layer of water on the surface of the prepared cavity must be accepted. This water layer reduces the surface energy and thus may reduce the wetting of the restorative material.
As referenced above, the most effective procedure for enhancing mechanical bonding commonly used by dentists is the acid-etch technique. The acid-etch technique has promoted the use of resin-based restorative materials because it provides a strong mechanical bond between resin and enamel/dentin (e.g., resin bonded metal retainers, porcelain inlaid veneers, and orthodontic braces). Accordingly, dentists typically use thermoplastic resins to restore and replace missing teeth. Most resin systems used in dentistry are based on methacrylates, and methyl methacrylate in particular.
Specifically, the process for bonding enamel and resin-based restorative materials involves the etching of the enamel to promote selective disintegration of the tooth enamel resulting in a microporous surface. Etched enamel (as opposed to normal enamel) is characterized by a high surface energy, and allows a resin to readily wet the surface and penetrate into the microporosity. Upon penetrating the microporosity of the etched enamel the resin can be polymerized to form a mechanical bond to the enamel. Polymerization occurs through a series of chemical reactions by which a macromolecule (i.e., polymer) is formed from large numbers of molecules known as monomers. Polymerization can occur either by series of localized reactions, commonly referred to as step growth polymerization, or by simple addition reactions, commonly referred to as addition polymerization. Most dental resins are polymerized by addition polymerization.
The resin projections (commonly referred to as "tags") may penetrate ten to twenty microns (.mu.) into the pores of the enamel, but their links are dependent on the enamel etching time. The standard acid used to produce the porous enamel is phosphoric acid at concentrations between thirty to fifty percent. Typically, dentists prefer an etchant in a gel form because the gel provides control over the exact placement of the etchant on the affected area. The application time of the etchant may vary depending on the degree of decay of the tooth. For example, a tooth having a high fluoride content resulting from fluoride treatment (i.e., treated water supply) may require a longer etching time as compared to a non-treated tooth. A common procedure includes applying the etchant for fifteen seconds.
Accordingly, upon etching the tooth, the dentist rinses the acid etchant off the enamel with a stream of water for approximately twenty seconds, then directs a jet of air across the affected area until the enamel and dentin is sufficiently dry. As discussed above, in order to form a sufficient bond the etched surface must be kept clean and dry until the dentist applies the resin. Because enamel etching raises the surface energy of the enamel, contamination can readily occur because of the tendency to reduce the energy level of the etched surface. A potential reduction in surface energy makes it more difficult to wet the surface with a bonding resin that may have a higher surface energy than that of the contaminated surface. Thus minimal contact with saliva or blood can prevent effective resin tag formation and severely reduce the bond strength.
Commonly used resins include acrylic resins, methyl methacrylate, poly methyl methacrylate, and multifunctional methacrylate and acrylate resins. Plasticizers are often added to resins to reduce the softening or fusion temperatures. Synthetic resins are popular restorative materials because they are insoluble, aesthetic, insensitive to dehydration, inexpensive, and relatively easy to manipulate. Modern composite materials are comprised of a resin matrix, inorganic filler particles, and additional components to enhance the effectiveness and durability of the material. For example, dentists oftentimes employ coupling agents such as silane to provide a bond between the inorganic filler particles in the resin matrix. Furthermore, an activator-initiator is necessary to polymerize the resin. Most dental composite materials are monomers that are aromatic or aliphatic acrylates. The most commonly used methacrylates in dental composites are bis-GMA, urethane dimethacrylate (UEDMA), and triethylene glycol dimethacrylate (TEGDMA) which polymarize by addition polymerization.
Historically composites were cured by chemically activated polymerization (often referred to as "self-curing") that had to be mixed. Disadvantages of self-curing composites include the presence of air bubbles resulting from the mixing process that inhibit polymerization and reduce control of the working time after the material has been mixed. Thus, a dentist was required to place the resin composite on the affected area of the tooth surface and shape the resin composite immediately following initiation of the polymerization phase. Accordingly, dentists employed a light source for activation of the initiator system. Advantageously, light cured materials allow the dentist to complete the placement and shaping of the composite before curing is initiated. Upon initiation, light curing generally requires only forty seconds of curing time to cure a two millimeter (mm) thick layer. In contrast, a chemically cured material requires several minutes to set.
Ultraviolet light cured composites have been replaced by visible light activating systems that have a greater ability to polymerize thicker increments up to two millimeters (mm). Light curable dental composites are typically supplied in a paste or gel form contained in a syringe. The free radical initiating system, consisting of the photo initiator molecule and an amine activator, is contained in the paste or gel. The two components do not interact until exposed to light capable of initiating polymerization. Exposure to light of the correct wavelength--approximately 468 nanometers (nm)--produces an excited state of the photoinitiator and an interaction with the amine to form free radicals that initiate addition polymerization. In visible light cured dental restorations, amines such as camphorquinone and dimethylaminoethylmethacrylate generate free radicals when irradiated by visible light. Modern light sources are provided by handheld devices that contain a light source and typically include a short rigid light guide made up of fused optical fibers. Preferred light sources usually include a tungsten-halogen light bulb.
Light activated materials provide a number of advantages over chemically activated resins. The light curable resins are single component pastes that require no mixing, thus the dentist controls the working time. Further, materials harden rapidly upon exposure to the curing light. Because the depth of cure depends on several variables (e.g., material and the location and quality of the light source), the restoration must be built up incrementally within each cavity. In other words, each increment must be cured before applying the next layer of resin. This stepwise procedure translates into an advantage in resin-composite restoration because a significant portion of the polymerization shrinkage is compensated for as the cavities being filled are cured.
Because a typical dentist's operatory lights emit radiation in the 400 to 500 nm range (i.e., sufficient to initiate polymerization of the resin-composite material), a dentist will not dispense the resin until it is to be used. Dentists use a number of applicator tools to insert the resin into the cavity. For example, dentists typically use a syringe that is separate and apart from the individual applicators for dispensing etchant, water, air, and light source. In brief, the goal is to minimize deformation of the resin during application. The dentist shapes the resin in the desired form and then cures the resulting incremental layer once each increment is inserted. Thereafter, additional increments are added, shaped, and cured.
Modern industry provides dentists with a variety of tools for performing dental restorations. The particular tool selected by the dentist is dependent upon the dental procedure. For example, a common dental tool is a multi-purpose syringe for dispensing various types of dental materials (e.g., anesthesia, resins, impression material, and epoxies.) Another common dental tool is an air and water syringe for delivering air, water and an air-water mix to an affected tooth during restoration. Yet another common dental tool is a fiber optic handpiece which incorporates a fiber optic handle and light source to facilitate illumination of the oral cavity and to cure light curable composites. Nevertheless, the above-referenced handpieces and syringes are generally separate units that must be manipulated by the dentist. Stated differently, the conventional handpieces and syringes must be stored on a storage rack, and retrieved separately each time the dentist begins a different step of the restoration procedure. The time between the removal of the handpiece or syringe from the proximity of the patient's mouth, the placement of the syringe upon the storage rack, the retrieval of a different syringe, and the placement of new tools proximate the patient's mouth for the next step is critical during restorative procedures. As discussed above, it is common for a patient to use his tongue to wet his mouth--and affected area--when the dentist removes a dental tool from the patient's mouth. Despite the use of suction devices, the accumulation of moisture on the affected area degrades the structural integrity of the resin and results in a poor quality filling that is prone to failure. It is understood by those skilled in the art that the variety of available handpieces and syringes, specifically directed to individual tasks (e.g., etching, rinsing, and curing), fail to promote the rapid etching and restoration of a tooth, thereby leading to contamination and poor bonding between tooth and resin.
Various connectors are used for connecting conduits for air, water, and power in a handpiece or syringe to supply the hoses of an instrument delivery unit. There are four types of standard connectors used in the United States. The connectors include the two-hole (commonly referred to as a "Borden connector"), a three-hole, and a four-hole connector. The four-hole connector (commonly referred to as a "Midwest connector") is the most popular connector. In a four-hole connector, the holes are for drive air, chip air, water, and exhaust. A five-hole connector is also available wherein the fifth hole represents a fiber optic bundle. For standardization purposes, hole locations are determined by an International Standards Organization (ISO) specification. The Borden two-hole connector supplies compressed air through the larger of the two holes and cold water through the smaller. The Midwest design has an exhaust tube for removing spent air and provides spray air and water separately. Many variations of these two main designs exist, for example, to supply electricity to motors or supply light to the fiber optics system of a hand piece. Most hand pieces are configured to allow rotation between hand piece and the connector in order to prevent the rubber supply hose from twisting the instrument during normal use. Most dentists prefer to use a handpiece attachment or fitting (commonly referred to as "a quick disconnect") designed to allow easy separation of the handpiece from supply tubing. Dentists prefer the handpiece and "quick disconnect" combination because sterilization of all handpieces and syringes between patients has become standard practice. Nevertheless, the individual dental tools for etching, rinsing, and curing fail to take advantage of the quick disconnect system. This lack of multifunction dental tools ignores the reality that most dentists prefer a single handpiece or syringe that can be transported from room to room.
The majority of all light activated materials used in restoration procedures are activated by blue light as opposed to ultraviolet light. Modern light curing devices generally utilize a fiber optic bundle which consists of many hundreds of fine glass optic fibers wherein each fiber is constructed from a fine core of glass surrounded by an envelope of glass of a different retracted index. Light traveling within the core bounces off the walls of the fiber and back into the core by total internal reflection. The light only leaves the bundle when it reaches the cut end surface of the core. Conventional light sources include a tungsten-halogen bulb placed into a separate and larger hand piece that shines the light via a short rigid light guide into the mouth onto the surface of the light activated material. The output of the light decreases according to the inverse square law. Accordingly, a short length fiber optic glass bundle is preferred because doubling the distance from the glass bundle will quarter the light density.
Nevertheless, the conventional handpieces and syringes described above fail to provide an integrated syringe for expediting the delivery of dental material, air, water, and light to the tooth structure during the restorative procedures. In particular, the conventional syringes either provide only air and water or only dental material. Furthermore, most light sources are independent of the dental material delivery instrument. In other words, the dentists must resort to at least two or three different instruments during a procedure, thus prolonging the contamination period of an etched tooth. Increased contamination equates to weak bonds between the resin and the tooth structure, thus leading to further decay or staining of the tooth. Therefore, there is a need for a syringe for enhancing the bonding of restorative materials to the tooth structure.
Therefore, there is also a need for a means for expediting the delivery of dental material, water, air, and curing light to the affected tooth structure in order to minimize contamination of the etched area.
Further still, there is a need for a single syringe containing a plurality of reservoirs for retaining various dental materials integral with means for delivering air, water, and curing light.